This project is concerned with the study of certain enzymes and other proteins that consist of multiple subunits and that assemble into macromolecular functional units. The glutamate dehydrogenases of vertebrates and of Neurospora crassa are enzymes of diverse properties that are regulated in different ways - the vertebrate ones by allosteric effectors, such as purine nucleoside di- and triphosphates, and those of Neurospora by the level of glutamate in the culture medium. Determination of the amino acid sequences and modification of specific amino acid residues permit the identification of binding sites for substrates, coenzymes and effectors and of residues concerned with assembly into the active enzymes. The phycobiliproteins of algae represent model organelle systems that consist of two types of chains that assemble spontaneously into cellular organelles. Studies on the structure and mode of assembly of these proteins is continuing. Studies are being performed on the cross-linking of histones to aid in understanding the relationships of these proteins to each other in the nucleosomes. Work has been initiated on the phosphorylated proteins of chromatin and on the kinases responsible for the phosphorylation.